One of our Aussie aircraft operators recently gave us notification of a perceived issue with magnetic riser covers (eg Sigma) interfering with compass calibration on jump planes. He states that the problem goes away as soon as the jumpers leave the plane. They have found that they can minimise the problem by not putting anyone with that equipment near the front of the plane. He feels that this is not a long term solution nor is it acceptable to continue operating with an unknown or variable quantity of magnetic interference in the aircraft.

So these covers have been in use for a few years now. Has anyone heard of any similar reports? (I have not) Specifically on whether there is any effect on aircraft compass calibration. If yes, has there been any resolution?

Kim Hardwick Technical Officer Australian Parachute Federation

(PS. One manufacturer has also been emailed directly. Just making this post as well to broaden the research net.)

One of our Aussie aircraft operators recently gave us notification of a perceived issue with magnetic riser covers (eg Sigma) interfering with compass calibration on jump planes.

Just a quick note - while magnetic riser covers (or any magnets, or any metal) can affect an aircraft's magnetic compass, none will affect an aircraft's directional gyro, which is what most pilots use as a compass. Traditionally the DG is aligned to runway heading before takeoff, and the magnetic compass is used only when the DG fails or precesses a bit during a long flight.

One of our Aussie aircraft operators recently gave us notification of a perceived issue with magnetic riser covers (eg Sigma) interfering with compass calibration on jump planes.

Just a quick note - while magnetic riser covers (or any magnets, or any metal) can affect an aircraft's magnetic compass, none will affect an aircraft's directional gyro, which is what most pilots use as a compass. Traditionally the DG is aligned to runway heading before takeoff, and the magnetic compass is used only when the DG fails or precesses a bit during a long flight.

Personally I set DG by compass and confirm runway heading before takeoff.

I'm not sure I see this as an issue. Magnetic deveation can come from a lot of sorces. It's also very dependent on the mounting and location of the compass. When we replaced the compass in my airplane we looked at changing it's mounting location. There wasn't enough athority in the adjustments to allow it. Every system on the aircraft affects it in one manner or another. Generally speeking it's set and calibrated in one perticular configuration ie. with the systems turned on in the configuration you would expect for IFR flight. Any change from that for example not haveing your nav lights on or not haveing all of your radios powerd up or turning the landing lights on will create an error. Even then in the best case there is ussally a writen table of corections in the plane, generally on a sticker under the compass.

Basically I don't see where this is such a big deal. Skydiving is generally a VFR activity conducted in a famillior local enviroment. Just deal with it. In the rare event that you are traveling cross country with jumpers on an extended flight, ferrying an air craft in IFR conditions just ask them to stow the rigs in the back.

Agreed! All skydiving flights should be VFR and close to home base, so directional instruments are not THAT important. Magnetic compasses are the third or fourth most important directional instrument, after: directional gyro, GPS, VOR and eyeball.

All skydiving flights should be VFR and close to home base, so directional instruments are not THAT important.

I just want to throw in that not all flights are VFR and some can't. For instance, high altitude jumps when you get into Class A airspace. No VFR there just IFR. Now for the most part that is not that common and most flights are VFR but that shouldn't rule out the importance of instruments.

Quote from the CI of the operation at which this issue was first observed/reported:

"This issue has emanated from my own DZ where we utilise a C-206. Up until 3 weeks ago we were jumping the original Sigmas with the Tuck Tab design Riser Covers, however we have slowly been upgrading with a retro-fit kit from UPT. So far we have only 3 out of 8 Sigmas with the modifications.

The original interference was noted by our pilot and was quickly diagnosed by the staff. There has been testing done by the staff and pilot in the meantime to find a workable solution to ensure the matter does not become a danger or inconvenience to anyone involve.

At this stage we are operating with a skeleton staff of 2 TMs which makes the issue a moot point as the seating arrangement with 2 Tms does not require the use of the seating bench that we have been using. The bench in question sits beside the pilot and is approximately 380mm tall and runs lengthwise from 300mm behind the leading edge of the rear door and forward to the dash. The problem only becomes clearly evident when the tallest TM (6'4") sits on the bench which bring the magnets in close proximity to the compass.

I have spoken to our pilot, who is monitoring the situation and will ensure that the situation does not cause any adverse effects to the operation of the compass.

A changing in the height of the bench is being investigated, so when we have 3 TMs in the aircraft, all will be able to remain out of the immediate proximity of the compass and prevent interference."

Like all gyroscopes, the directional gyro or heading indicator will have a drift after a certain time, therefore the directional gyro or heading indicator has to be reset manually every 15-20 minutes to match the compass when flying. Provided being in a straight level flight, the compass is a reliable device and has to be calibrated every 12 months by an aviation mechanics. The mechanics establishes a compass correction card as well mentionning if the correction was been done with radio on or off. The airplane compass has also a logbook to record each calibration. I am surprised to read that the use of compass in aviation seems to be old fashion for some readers. When you lose electrical power on an airplane (that happened to me), you lose the vaccum pump which drives all gyroscopic devices including the DG but your compass is still working. I am speaking about Cessna airplanes but basically, other airplanes have similar systems.

Yea, I remember doing compass turns during instrument training and yes it's a tool in the tool box but in this day and age if your relying on a compass as your only backup you shouldn't be in the clouds, and you sure don't need one to fly jumpers.

Set the DG to runway heading and climb for 20 minutes and your problem jumps out.

BTW I have the DB COOPER #290 certificate from jumping out of the Boeing 727 in 1992 at Quincy Ill. We were 180 people in the airplane. I jumped it again in 1998. Later on I added the DC9 by doing two jumps out of it in 2006 at Rantoul Ill.